Superior cervical ganglionectomy in monkeys: light and electron microscopy of the anterior eye segment

Morphological changes in the anterior eye segment of eight cynomolgus monkeys were investigated 2 days to 2.2 years after unilateral surgical superior cervical ganglionectomy (SCGx). SCGx was confirmed by histologic examination of the excised surgical specimen and persistent ipsilateral miosis. In four short-term monkeys (2, 4, 7 and 11 days), iris, ciliary muscle and trabecular meshwork were studied by electron microscopy. In the other four longer-term monkeys (3 week, 4 week, 5 week, 2.2 year) the anterior eye segment was investigated with tyrosine hydroxylase immunohistochemistry (TH-IR) and catecholamine fluorescence (CF). Electron microscopy of experimental eyes showed characteristic signs of Wallerian degeneration in numerous nerve fibers and terminals in the iris, but to a lesser extent in the ciliary muscle and the trabecular meshwork. TH-IR and CF showed marked interindividual differences. In all experimental eyes, there was a marked reduction, but never a complete absence of adrenergic nerves in the iris. In two animals (4 week and 2.2 years), the adrenergic innervation of the ciliary body and the chamber angle was similarly reduced. In contrast, in the experimental eyes of the other two animals (3 and 5 weeks), changes in adrenergic innervation to the ciliary body and chamber angle were minimal or absent. The results indicate that following apparently complete SCGx in the cynomolgus monkey, reduction of adrenergic innervation to the iris as evidenced by pupillary physiology, electron microscopy, TH-IR and CF does not guarantee reduction in adrenergic innervation to the ciliary body and trabecular meshwork. SCGx may not extirpate all third order sympathetic neurons in the distal stump, or there may be a significant contribution of accessory ganglion cells to the adrenergic innervation of the anterior eye segment.

Scanning electron microscopic study of episcleral arteriovenous anastomoses in the owl and cynomolgus monkey

In the present study we have analyzed the architecture of the episcleral microvasculature in the owl and cynomolgus monkey using scanning electron microscopy of resin casts. Due to the topical pretreatment with nitroprusside the complete vasculature including segments of the aqueous humor outflow channels could be visualized. We found that 1-3 mm posterior to the limbus corneae the episcleral vessels form numerous arteriovenous anastomoses (AVA) in the size of small arterioles and venules. These AVA are also located at the collector channels near Schlemm's canal and at the episcleral venous plexus which drains the collector channels. It is assumed that the AVA might influence not only the circulation in the episcleral venous plexus but also in the aqueous humor outflow routes.

Short-term hemodynamic changes in episcleral arteriovenous anastomoses correlate with venous pressure and IOP changes in the albino rabbit

In the present study we have determined the effects of acute diameter changes in the recently discovered episcleral arteriovenous anastomoses (AVA) on episcleral venous pressure and intraocular pressure (IOP) in the rabbit eye. The pressure was measured in episcleral arterioles, AVA and veins (vascular pressure) with a pressure chamber mounted on the tip of a microendoscope. After constriction of the AVA following topical administration (100 micrograms) of epinephrine we observed a decrease in the episcleral vascular pressure as well as in the IOP. Acute widening of the AVA after topical administration of 5mg nitroprusside led to a significant increase in the pressure of arterioles, AVA, veins and IOP which lasted several min. After 0.5mg topical nitroprusside the blood flow in the AVA increased. No significant effects were seen in the intravascular pressures; the IOP had a tendency to decrease. Experimental lowering of the IOP to 10mmHg caused an increase of vascular diameters and of blood flow in the AVA. It is assumed that-at least in drastic hemodynamic disorders-the degree of the AVA-perfusion might influence aqueous humor outflow and IOP due to changes of the episcleral venous pressure.

Functional morphology of the episcleral vasculature in rabbits and dogs: presence of arteriovenous anastomoses

Scanning electron microscopic analysis of corrosion casts of the intra- and episcleral vasculature in the limbic region of two species (rabbit and dog) revealed typical arteriovenous anastomoses representing shunts between the long radial arterioles, branches of the anterior ciliary arteries, and the episcleral venous plexus. The arteriovenous anastomoses consist of a small arteriolar segment and a wide, funnel-like venous segment. Using immunohistochemical techniques it was shown that the wall of the arteriolar segment consists of smooth muscle cells containing alpha-smooth muscle actin. In the dog, the vessel wall of the arteriovenous anastomoses also contain typical epithelioid cells, the structure of which was analyzed by transmission electron microscopy. In the episcleral vasculature, a capillary network is lacking, an elaborate wide venous plexus is developed instead. It is assumed that this plexus with the help of the newly described arteriovenous anastomoses may influence aqueous humor drainage and thereby also intraocular pressure.

In vivo observations of the episcleral vasculature in the albino rabbit

The recently described arteriovenous anastomoses of the episcleral vasculature were studied in the albino rabbit by in vivo microscopy and microendoscopy. The arteriovenous anastomoses lead directly into the episcleral venous plexus which drains aqueous humor via well-visible aqueous veins. In the arteriolar segment of the arteriovenous anastomoses the blood flow velocity, measured by intra-arterial bolus injections of Evans blue, decreases drastically toward the venular segment of the arteriovenous anastomoses. After topical application of epinephrine, the arteriolar segment contracts faster and to a greater degree than all other parts of the episcleral vasculature. In the aqueous veins this stoppage of the blood inflow from the arteriovenous anastomoses may allow an increase in the amount of aqueous humor drained from the anterior chamber. The simultaneously measured intraocular pressure decreases significantly. Experimental elevation of the intraocular pressure from 18 to 30 mm Hg causes a decrease in diameter and blood flow in the arteriovenous anastomoses. These effects are reversed by returning to normal intraocular pressure levels. It is assumed that the arteriovenous anastomoses play a role in aqueous humor drainage by the episcleral venous plexus.

Ultrastructure of the trabecular meshwork in untreated cases of primary open-angle glaucoma (POAG)

Thirty-one trabeculectomy specimens of patients suffering from primary open-angle glaucoma (POAG) who had received no, or only minor, medication prior to surgery were ultrastructurally and quantitatively analysed. Most of the specimens revealed thickened trabeculae, increased amounts of plaque-material deposited within the cribriform layer and an abundance of long spacing (lattice) collagen. The uveal meshwork was partly deprived of cells whereas the cribriform layer often contained numerous enlarged, light cells with many small mitochondria and lysosomes but no prominent endoplasmic reticulum or Golgi complexes. The quantitation of sheath-deprived plaque material (SD plaques) in a defined area of inner and outer wall of Schlemm's canal showed no significant difference between the untreated cases studied here and the treated ones studied previously. However, both groups had significantly higher amounts of SD plaque material in the inner wall than normal controls of a similar age range.

[Immunocytochemical and ultrastructural studies of human scleral spur. Characterization of a contractile cell population]

Contraction of the ciliary muscle induced by cholinergic drugs causes movement of the scleral spur and separation of the trabecular meshwork lamellae. The effect of epinephrine, however, does not seem to be mediated by ciliary muscle tone. We investigated the scleral spur in 37 human eyes (age 17-87 years). Serial tangential sections were studied with ultrastructural and immunocytochemical methods. The ciliary muscle cells do not enter the scleral spur, but their tendons, which consist of elastic fibers, are continuous with the elastic fibers in the scleral spur. Within the scleral spur is found a population of circularly oriented and spindle-shaped cells. The scleral spur cells form no bundles, but are loosely aggregated. They have long cytoplasmic processes and are connected to each other by adherence type and gap junctions. The scleral spur cells show intense staining for smooth-muscle-specific alpha-actin and myosin. Ultrastructurally, the scleral spur cells contain abundant actin filaments, but otherwise do not show the typical ultrastructure of ciliary muscle cells. The scleral spur cells do not express a complete basal lamina. They form individual tendinous connections with the elastic fibers in the scleral spur, which are continuous with the elastic fibers of the trabecular meshwork. The scleral spur cells are in close contact with nerve terminals containing small granular vesicles that are typical for adrenergic terminals. We conclude that the scleral spur cells are contractile myofibroblasts. Their contraction might be involved in the effects of epinephrine on the aqueous outflow.

Postnatal development of skull base, neuro- and viscerocranium in man and monkey: morphometric evaluation of CT scans and radiograms

Postnatal development of the neuro- and viscerocranium with special reference to the maxillodental structures was studied morphometrically by analyzing computer tomograms and radiograms of human and monkey heads of different age groups. The following parameters were used: the prognathic angle, the clivus angle, the palate-incisivus angle, the interincisival angle and the viscerocranial quotient. In the newborn primates including man, all parameters measured were relatively similar; postnatally, however, characteristic differences in the growth pattern between man and monkey were developing. In monkey, a marked prognathic growth of the viscerocranium was found associated with characteristic positional changes of the frontal teeth, whereas the growth of the neurocranium was retarded. Here, unlike the human, a flattening of the skull base was observed. In contrast, the human skull showed no major proportional changes during its postnatal development compared with the original spherical skull form of the newborn.

Contractile cells in the human scleral spur

The scleral spur in 37 human (age 17-87 years) and six cynomolgus monkey eyes (2-4 years) was investigated. Serial meridional and tangential sections were studied with ultrastructural and immunocytochemical methods. The bundles of the ciliary muscle do not enter the scleral spur, but their tendons, which consist of elastic fibres join the elastic fibres in the scleral spur. Within the scleral spur a population of circularly oriented and spindle-shaped cells is found. In contrast to the ciliary muscle cells, the scleral spur cells form no bundles, but are loosely aggregated. They have long cytoplasmic processes and are connected to each other by adherens-type and gap junctions. They stain intensely for alpha-smooth muscle actin, myosin and vimentin. In contrast to the ciliary muscle cells, they do not stain for desmin. Ultrastructurally, the scleral spur cells contain abundant thin (actin) filaments, but do not otherwise show the typical ultrastructural features of ciliary muscle cells. The scleral spur cells do not express a complete basal lamina. They form individual tendinous connections with the elastic fibres in the scleral spur, which are continuous with the elastic fibres of the trabecular meshwork. The scleral spur cells are in close contact with nerve terminals containing small agranular (30-60 nm) and large granular (65-110 nm) vesicles but also with terminals containing small granular (30-60 nm) vesicles which are regarded as typical for adrenergic terminals. We conclude that the scleral spur cells are contractile myofibroblasts. Their contraction might influence the rate of the aqueous outflow.

Age-related changes of the human ciliary muscle. A quantitative morphometric study

The age-related changes of the ciliary muscle of human eyes (33-87 years) were studied on histological meridional sections. Eighty-five melanoma eyes and 10 eyes of normal donors were investigated. The total area and the length of the muscle, the area of the three main portions and the distance of the inner apex of the muscle to the scleral spur were determined and correlated with age. Total area and length of the muscle show a continuous and significant decrease with age. The area of the longitudinal and reticular portion continuously decreases, whereas the area of the circular portion significantly increases with age. The decrease in area is more pronounced in the longitudinal portion than in the reticular portion of the muscle, which shows an age-related increase in connective tissue. In addition, the distance of the inner apex of the muscle to the scleral spur shortens continuously. Thus, with increasing age the ciliary muscle adopts an anterior-inward position. A similar form is seen in young eyes after ciliary muscle contraction only. There might be a functional relationship between the observed age-changes in the ciliary muscle system and the phenomenon of the so-called 'lens paradox' (steepening of the anterior and posterior curvatures of the disaccommodated lens with age).

The effect of epinephrine on ciliary process vasculature and IOP studied by intraocular microendoscopy in the albino rabbit

The effect of epinephrine on intraocular pressure (IOP) and the hemodynamics of the ciliary process vasculature in albino rabbits was studied by intraocular microendoscopy. Intraarterial application of epinephrine (15, 50, 250 ng/kg bw) lead to an immediate vasoconstriction and a reduction in blood flow velocity (BFV) in the iridial and major ciliary processes lasting from 30 to 120 sec. This anemic phase was followed by a hyperemic phase of about 60 to 240 sec. showing a vasodilation up to 150% of the initial diameters and an increase in BFV. The hyperemic phase can be prevented by pretreatment with indomethacin. Simultaneously measured IOP decreases in the anemic and increases in the hyperemic phase parallel with the changes in vascular diameter. After topical administration of epinephrine (25-50 micrograms/kg bw) a marked vasoconstriction followed by a vasodilatory phase was similarly found. However, the reactive changes of the ciliary process vasculature lasted considerably longer. The anemic phase lasted 15 minutes, the hyperemic phase 40 to 60 min. Again, this hyperemia can be prevented by indomethacin-pretreatment. In the iridial processes the anemic phase persisted till 70 minutes. No hyperemia and no substantial influence of indomethacin-pretreatment was found in this territory. In the anemic phase the IOP decreased in average from 20 mmHg to 15 mmHg. However, in contrast to the reactive changes of the IOP after intraarterial epinephrine application, the IOP did not increase again in the hyperemic phase, but decreased further to about 12 mmHg. After pretreatment with indomethacin the IOP remained at the level of 15 mmHg. The short-term IOP-changes after i.a. application of epinephrine, mirror the vasoconstrictory and vasodilatory reactions in the ciliary processes and might be due to volume changes in the eye (plethysmographic effect). However, the long lasting IOP reduction after topical epinephrine in the hyperemic phase can not be due to vascular reactions in the ciliary processes. There must be other factors responsible for the long lasting pressure reducing effect of epinephrine.

The craniofacial proportions and laryngeal position in monkeys and man of different ages (a morphometric study based on CT-scans and radiographs)

Using CT-scans and radiographs, sagittal planes through the head and neck of men and monkeys at different ages were analyzed morphometrically for their craniofacial proportions and laryngeal position. In monkeys, a continuous prognathic growth of the splanchnocranium was found within the first 3 years. The neurocranial growth, however, was markedly reduced. The larynx of monkeys showed only a slight descensus with age. In contrast to this, the growth of the splanchnocranium in man did not change the craniofacial proportions significantly. The larynx, however, descended markedly within the first two years of life. In adults, the final position of the larynx was nearly 3 vertebral bodies further caudally than in the newborn. The differences in the postnatal position of the larynx, which is essential for the development of speech, are explained by differences in the growth pattern of human and monkey skulls.

Outflow facility studies in the perfused human ocular anterior segment

We have recently developed a tissue model of the human aqueous outflow pathway involving placement of the eviscerated anterior corneoscleral shell, [with lens and uveal tissue removed but trabecular meshwork (TM) attached] onto a specialized perfusion apparatus. The TM and associated outflow tissues are perfused with culture medium at a physiologically-relevant perfusion pressure in a 5% CO2 environment at 37 degrees C. Under these conditions, the perfused outflow tissues are similar for several days, to the human and/or subhuman primate outflow system in vivo with regard to morphology as well as several functional parameters. Measured facility of outflow (0.271 +/- 0.018 microliters min-1 mmHg-1, n = 79) is similar to facility values obtained by tonography in living human beings. Moreover, outflow facility decreases in a linear fashion with increased perfusion pressure by 1.4% mmHg-1. Finally the removal of the TM results in a 41% decrease in measured outflow resistance. The ability to study viable human outflow tissue for at least several days and the opportunity to establish a model which serves as an alternative to animal testing, point to the potential importance of this technique in investigating the biology of the aqueous outflow system.

Parasympathetic denervation of the ciliary muscle following panretinal photocoagulation

Cynomolgus monkeys underwent unilateral panretinal scatter photocoagulation (PRP) and/or nasal and temporal horizontal retinal meridional photocoagulation (HRMP) with xenon arc or argon or krypton laser light. Shortly thereafter, in the PRP-treated eyes, accommodative responsiveness to topical eserine and electrical stimulation of the Edinger-Westphal nucleus (EWN) was diminished, accommodative responsiveness to intramuscular (i.m.) pilocarpine was enhanced, and the number of muscarinic receptors in the ciliary muscle was reduced compared to the contralateral controls. In most instances, these parameters returned to normal over 6-12 wks and the abnormalities could be induced again by another round of PRP. However, in some PRP-treated eyes, accommodative responsiveness to EWN stimulation and topical eserine remained subnormal permanently (greater than 1 yr). Shortly after HRMP alone, accommodative responses to i.m. pilocarpine, topical eserine, and central stimulation did not differ markedly in the treated and control eyes. Morphologic studies 1 to 78 wk following PRP revealed that myelinated and unmyelinated nerves within the entire circumference of the choroid and ciliary muscle were severely damaged early on. The number of unmyelinated nerves between the individual ciliary muscle fibers was drastically reduced, those which remained were swollen or deteriorated, and agranular synaptic vesicles were rarely seen. Thereafter, the nerves in the choroid and ciliary muscle gradually regenerated. Following HRMP, only the choroidal nerves which passed through the photocoagulated areas and the ciliary muscle nerves in the corresponding meridians showed signs of deterioration, and there was minimal effect on the physiologic responses examined. These findings collectively indicate that intraocular parasympathetic denervation of the ciliary muscle is produced by PRP, although all nerve types are likely damaged.

Posterior attachment of ciliary muscle in young, accommodating old, presbyopic monkeys

The authors studied the posterior attachment of the ciliary muscle in seven young (3-10 yr) and five old (26-34 yr) rhesus monkeys by light microscopy and electron microscopy. Posterior attachment of the muscle bundles consisted of elastic tendons, exclusively. The elastic tendons were continuous with the elastic lamina of Bruch's membrane and were also connected by smaller elastic fibers to an elastic meshwork that surrounds the pars plana vessels. In some areas, the tendons formed focal contacts with the endothelial cells. The authors found that in old eyes, the tendons and the elastic fibers of the posterior ciliary body showed pronounced structural changes. The tendons appeared thickened, showed increased amounts of associated microfibrils, and were surrounded by dense layers of thick collagen fibrils. An increased amount of collagen fibrils was also seen between the elastic layer of Bruch's membrane and the pigmented epithelium. A mechanical link between those collagen fibrils and the elastic fibers is suggested by the presence of osmiophilic points of contact. The age-related increase in elastic fibrillar material could cause decreased compliance of the posterior insertion of ciliary muscle and could be an essential factor for presbyopia in rhesus monkeys.

Spectrometric measurements in the anterior eye vasculature of the albino rabbit--a study with the EMPHO I

Intracapillary haemoglobin oxygenation (oxygen saturation) and haemoglobin concentration (corresponding with blood volume) were measured in different regions of the albino rabbit anterior eye segment using the Erlangen micro-lightguide spectrophotometer (EMPHO I). The tip of the microlightguide (active diameter 210 microns, cover diameter 0.5 mm) was placed in the vitreous by a goniometric mounting and controlled by a micromanipulator. After stepwise elevation of intraocular pressure (IOP) the haemoglobin oxygenation decreased slightly in the iris at an IOP-level of 60 mmHg, whereas in the three regions of the ciliary processes and in the peripheral choroid haemoglobin oxygenation did not decrease until values of 80 mmHg were applied. In contrast, haemoglobin concentration decreases when the IOP increases in all regions except in the pars plana where the haemoglobin concentration increased at 40 and 60 mmHg. The most pronounced reactive hyperaemia was found in the major ciliary processes. Quite passive changes of haemoglobin concentration were seen in the peripheral choroid. Effective regulatory mechanisms must exist which result in IOP-independent (20-60 mmHg) haemoglobin oxygenation, whereas pronounced changes in intracapillary haemoglobin concentration were observed. The decay of both parameters at IOP 80 mmHg is indicative of an exhaustion of their regulatory capacity. Epinephrine topically applied onto the conjunctival sac or injected into the common carotid artery led to a short-term decrease of haemoglobin concentration and, later, a hyperaemic response. A short-term haemoglobin deoxygenation was found especially in the major ciliary processes.

Scanning electron microscopic study on the vasculature of the human anterior eye segment, especially with respect to the ciliary processes

The architecture of the vasculature of the human anterior eye segment was studied by scanning electron microscopy of vascular resin casts. Regarding the major vessels it was found that the perforating branches of the anterior ciliary arteries (ACA) form an anastomozing circle which lies in the posterior portion of the ciliary muscle (intramuscular circle). The ACAs supply the outer and posterior parts of the ciliary muscle, partly the iris, and the peripheral choroid by recurrent ACA branches. The major arterial circle of iris (MACI) which lies more anteriorly is formed mainly by the long posterior ciliary arteries and supplies the inner and anterior portion of the ciliary muscle, the iris and the ciliary processes. The ciliary process vasculature consists of three different vascular territories with discrete arterioles and venules. The first vascular territory which is located at the anterior end of the major processes, is drained posteriorly by venules which pass the ciliary body without greater connections to the venules of the major ciliary processes. The second and third territories comprise the vasculature of the major and minor ciliary processes drained posteriorly by venules which are located at the margin of the ciliary processes. In supravital experiments with human autopsy eyes, a characteristic segment of arterioles supplying the first and second territory was found to be constricted after immersion with epinephrine in a similar way as in cynomolgus monkeys in vivo. Although the general arrangement of the ciliary process vessels is similar to that of the cynomolgus monkey, there are characteristic differences in the size of the territories and in the pattern of the capillary networks. The division of the ciliary process vasculature into three vascular territories may reflect a functional differentiation in the process of aqueous humour production.

Age-related changes of the ciliary muscle in comparison with changes induced by treatment with prostaglandin F2 alpha. An ultrastructural study in rhesus and cynomolgus monkeys

The relationship between individual ciliary muscle cells and the surrounding connective tissue was studied in the eyes of three normal, young (3-4 years) cynomolgus monkeys (Macaca fascicularis), three aged (34-36 years) rhesus monkeys (Macaca mulatta) and seven young (3-7 years) cynomolgus monkeys topically treated with prostaglandin F2 alpha (PGF2 alpha) for 4-8 days. In normal eyes, collagen fibrils and microfibrils are in places in continuity with the muscle cells' basal lamina, which is connected to the cell membrane by fine fibrillous material. In old eyes, the basal lamina is markedly thickened, masking the connection of fibrils with the muscle cells' membrane. A distinctive finding in several muscle cells of old eyes are electronlucent clefts, 60-80 nm wide, between basal lamina and cell membrane, which are not transversed by fibrils or fibrillous material. The cell membrane of these muscle cells shows large folds filled with disarranged myofilaments. Additionally, these cells contain inclusion bodies consisting of concentrically arranged double membranes. Following treatment with PGF2 alpha, similar changes are seen in young animals, too. Here, the muscle cells have lost their connection to the extracellular fibrils due to a PGF2 alpha-induced lysis of extracellular material. Lack of attachment between basal lamina and altered muscle cells in aged eyes might indicate an involvement of the extracellular matrix in age-related changes of the individual ciliary muscle cells.

Ciliary neuromuscular morphology in cynomolgus monkeys after ciliary ganglionectomy

Cynomolgus monkeys underwent unilateral ciliary ganglionectomy (CG) and/or posterior ciliary neurectomy (PCN). The ciliary muscle was functionally denervated, as evidenced by loss of choline acetyltransferase activity, loss of the accommodative response to topical eserine and electrical stimulation of the Edinger-Westphal nucleus, and supersensitivity of the accommodative response to pilocarpine. Light and electron microscopy carried out 3-28 days after CG/PCN revealed degeneration of myelinated and unmyelinated nerve fibers as evidenced by axonal swelling and shrinkage, mitochondrial degeneration, axoplasmic condensation and vacuolization, and activated, phagocytosing Schwann cells. By 1-3 months after CG/PCN, few non-myelinated axons remained between the muscle bundles, larger nerve bundles were disordered and deteriorated, and Schwann cells filled with lipid and cellular debris were prominent. Beyond 6 months (6-37 months), most eyes were reinnervated by functional criteria. Concurrently, the ciliary neuromuscular morphology appeared virtually normal, exhibiting many non-myelinated axons containing numerous agranular synaptic vesicles and large mitochondria; however, remnants of degenerated axons were still present. In two eyes remaining functionally denervated, many of the unmyelinated axons between the ciliary muscle bundles were swollen or empty, with small, degenerated mitochondria and only rare synaptic vesicles, and were often ensheathed by thickened, condensed Schwann-cell cytoplasm. The muscle fibers were atrophic and separated from each other as well as from the ensheathed nerve fibers. Thus, following CG/PCN, the morphologic and functional evidence of parasympathetic denervation and reinnervation of the ciliary muscle is pathophysiologically and temporally consistent.

In vitro cultures of trabecular meshwork cells of the human eye as a model system for the study of cellular aging

Cells from the human trabecular meshwork providing a drainage system for the outflow of aqueous humour in the eye were isolated and propagated in monolayer culture. Following serial subcultivation of the primary cultures, there was a gradual decline in the fraction of dividing cells with increasing population doubling level (PDL) resulting finally in growth cessation and disintegration of these 'senescent' cultures. The number of population doublings was at most 20. Senescent cultures revealed reduced glycosaminoglycan synthesis rates (as measured by [14C]glucosamine incorporation) with a relative decrease of hyaluronic acid and increase of heparan sulfate. Medium-supplied (exogenous) hyaluronic acid enhanced hyaluronic acid synthesis of trabecular meshwork cells cultured in a defined, serum-free medium. Ascorbic acid (25-200 micrograms/ml), which is found in very high concentration in the ocular aqueous humour, stimulated hyaluronic acid synthesis of confluent cultures, also. The functional significance of decreased hyaluronic acid (and elevated heparan sulfate) synthesis in the process of cellular aging in vitro (and in vivo?), as well as the importance of hyaluronic acid for the structural integrity and functional activity of the trabecular meshwork were discussed.

Oxygen delivery to the anterior chamber of the eye--a novel function of the anterior iris surface

By means of pO2-needle electrodes the oxygen tension in the anterior chamber of rabbit and cynomolgus monkey eyes was measured and correlated with the topography. It can be clearly shown that the pO2 in front of the pupil is substantially lower than in front of the anterior iris surface. It is evident that the O2-supply of the anterior chamber is provided by the iris vasculature. This result was confirmed by measurements after partial or total iridectomy. A brief recapitulation of the morphology of the iris showed that the abundance of iris vasculature is well understandable in view of these pO2 measurements.

Functional morphology of accommodation in the raccoon

The raccoon (Procyon lotor) is a small carnivore which eats in the upright position, using hand- and finger-like front paws and digits to wash, hold and examine its food at close range. These anatomic and behavioral characteristics prompted structural and functional studies of the accommodative capability of this species. By light and electron microscopy, we observed a prominent ciliary smooth muscle and zonular apparatus. When stimulated by carbachol or pilocarpine, the muscle and zonular apparatus exhibited a shift from longitudinal to reticular or circular orientation of some ciliary muscle bundles, anterior movement of the muscle as a whole, and more oblique crossing of the zonular fiber bundles in the zonular plexus. Maximum carbachol-induced accommodative amplitude measured by coincidence refractometry ranged from 3 to 19 diopters in these 1 to 9 yr old animals, with no definite age-accommodation relationship. A-scan ultrasonographic biometry showed that during accommodation the lens thickened very little, if at all, but moved anteriorly, while the apparent cornea to retina distance increased slightly. The raccoon thus exhibits the greatest accommodative capability of any non-primate terrestrial mammal so far studied.

Microendoscopy of the anterior segment vasculature in the rabbit eye

Intraocular microendoscopy is introduced as a new method which allows a direct in vivo observation of the microvasculature of the eye. Using video equipment, a quantitative evaluation of changes in vessel diameters, e.g. after administration of vasoactive agents, and an estimation of blood oxygenation are possible. Experimental studies with fluorescent dyes can also be performed using special filters. In albino rabbits, no apparent vascular disturbances were observed under certain experimental conditions. Touching a ciliary process with the tip of the endoscope immediately resulted in a vasodilation and stoppage of blood flow, surprisingly in the affected area only. After epinephrine, the locally traumatized ciliary processes remained unchanged while the vessels of the neighboring ciliary processes constricted intensely. After reduction of the intraocular pressure the major ciliary processes began to swell. A leakage of fluorescein-dextran was only found in the iridial ciliary processes.

SEM studies of the functional morphology of the ciliary process vasculature in the cynomolgus monkey: reactions after application of epinephrine

In the ciliary processes of the cynomolgus monkey three vascular territories with discrete arterioles and venules were found by means of scanning electron micrographs of vascular resin casts. The first vascular territory, which is located at the anterior end of the major processes, is drained posteriorly by long isolated venules, which pass the ciliary body without greater connections to the venules of the major ciliary processes, whereas the second and third territories comprise the vasculature of the major and minor ciliary processes drained posteriorly by veins which are located at the internal edge of the ciliary processes. With the functional resin casting method it could be demonstrated that 15 min after application of 20 micrograms of epinephrine into the conjunctival sac the terminal arterioles supplying the first vascular territory constricted most intensely, whereas the terminal arterioles related to the middle and posterior vascular territory of the ciliary processes constricted to a lesser extent. Twenty-five minutes after topical application of epinephrine only the posterior vascular territory and the capillaries of the ciliary muscle appeared filled in the resin casts. The vasculature of the anterior territories remained empty because of strong vasoconstriction of the supplying arterioles. The three morphologically different vascular territories with their different sensitivities to epinephrine may reflect a functional differentiation in respect to aqueous humour formation and resorption.

Outflow facility studies in the perfused bovine aqueous outflow pathways

We have recently developed a technique for constant pressure perfusion of the aqueous outflow pathway of the eye. Our preliminary studies, conducted in the calf eye, show surprisingly that the manipulations necessary for preparing the outflow pathways and attached corneoscleral shell for perfusion do not greatly disrupt normal aqueous outflow physiology and anatomy according to the following criteria: 1. facility of outflow is similar before and during outflow pathway perfusion 2. as in the intact eye, facility of outflow decreases with increased IOP 3. removal of outflow resistance tissue greatly increases facility of outflow 4. morphology of outflow tissues remains normal Use of the perfused outflow pathway model may enable the creation of valuable in vitro preparations which may provide much needed information about the pathogenesis of primary open-angle glaucoma.

Reactions of efferent venous segments in the ciliary process vasculature of albino rabbits

In albino rabbits, the reactions of a defined venous segment of the ciliary process vasculature to vasoactive agents were studied using our new technique of in vivo microendoscopy and using supravital specimens of the anterior eye. This segment is situated in the pars plana of the ciliary body and is the continuation of the venules at the inner edge of the minor and major ciliary processes which posteriorly drain the blood in the veins of the peripheral choroid. Three- to 4 min after administration of carbachol, a constriction of this efferent venous segment was seen in the in vivo microendoscopy as well as in supravital specimens. The adjacent vessel segments remained relatively unchanged. Two- to 3 min after intra-arterial administration of atriopeptin (ANP), an intense constriction of the efferent venous segment, followed by a reactive hyperaemia, was found by in vivo microendoscopy. The iris veins which collect the blood from the iris and the iridial ciliary processes pass the pars plana without touching the ciliary process vasculature. No reactions to the vasoactive agents tested were observed in these vessels. It has been concluded that the efferent venous segment of the ciliary process may play a role in the regulation of perfusion pressure within the ciliary process capillaries.

Intraocular microendoscopy of the ciliary-process vasculature in albino rabbits: effects of vasoactive agents

The reactions of the ciliary-process microvasculature following administration of various vasoactive substances were studied in the albino rabbit using a new method of intraocular microendoscopy. This technique allows an in vivo observation of arterioles, capillaries and venules of the ciliary body and iris. As long as these tissues are not traumatized, the newly described method of intraocular microendoscopy produces no reactive changes in the vasculature. The video images of microendoscopy were also evaluated quantitatively. Administration of substance P caused a short-term ischemic phase in the ciliary-process vasculature which preceded a long-term hyperaemia. After topical administration of epinephrine as well as intra-arterial administration of epinephrine, phenylephrine and isoproterenol, rapid and intense vasoconstrictory or vasodilatory reactions were seen in the terminal arterioles of the vascular territories in the ciliary processes. The terminal arterioles of the iridial ciliary processes responded faster and more intensely than those of the major ciliary processes. It is concluded that the terminal arterioles play an important role in blood-flow regulation of the ciliary processes and function as special afferent vessel segments which control the circulation within the ciliary-process capillaries.

SEM studies on the functional morphology of the rabbit ciliary process vasculature

Architecture and functional reactions of the blood vessels of the rabbit ciliary processes were studied after administration of epinephrine and isoproterenol. A new corrosion cast technique was applied which allows the analysis of different functional stages in the vascular system by scanning electron microscopy. The ciliary process vasculature is divided into three different vascular territories, each supplied by individual arterioles: (1) the iridial ciliary processes; (2) the anterior (pre-lenticular) portion of the major ciliary processes; and (3) the minor ciliary processes localized post-lenticularly between the major processes. The three vascular territories differ not only in form and architecture of the capillaries but also in their reactions on vasoactive agents. After epinephrine, the earliest reactions were seen in the first vascular territory followed by the second, the third vascular territory being least sensitive. The most intense vasoconstrictory changes were found in the terminal arterioles which supply each vascular territory separately. This afferent vascular segment might therefore be considered to be the most important structure for regulation of blood flow through the ciliary processes.

Exogenous glycosaminoglycans stimulate hyaluronic acid synthesis by cultured human trabecular-meshwork cells

Addition of hyaluronic acid (50-200 micrograms ml-1) to the defined, serum-free media of cultured human trabecular-meshwork cells resulted in an increase of glycosaminoglycan (GAG) synthesis as measured by the incorporation of [14C]glucosamine. Lesser stimulatory effects were exerted by dermatan sulfate and chondroitin-4- or -6-sulfate. Nearly 90% of the labeled GAGs were found to be exerted into the medium and ea. 10% were associated with the cell layer. Mainly hyaluronic acid synthesis was stimulated by the exogenous GAGs. Analysis of the GAG-pattern revealed that exogenous hyaluronic acid stimulated hyaluronic acid synthesis (positive feedback), while exogenous dermatan sulfate and chondroitin sulfate had additional effects on chondroitin sulfate synthesis. Cell growth of these cultures, which exhibited a limited proliferative capacity (ca. 18 population doublings during their life span) was not affected by the GAG treatment. Thus, exogenous hyaluronic acid and to a lower degree dermatan sulfate or chondroitin sulfate appeared to interfere with the GAG-metabolism of these human trabecular-meshwork cells in culture.

Quantitative analysis of 'plaque material' between ciliary muscle tips in normal- and glaucomatous eyes

Between the anterior ciliary muscle tips in normal and glaucomatous eyes, different forms of plaque material were found within the intermuscular connective tissue. These plaques derive from either the sheaths of the elastic-like fibers or the elastic tendons of the anterior ciliary muscle tips. In addition, there are plaques which have the characteristics of the hyalinized basement membranes of the trabecular beams. The quantitative evaluation of all three types of ciliary muscle (c.m.) plaques showed that in normal eyes the amount of c.m. plaques increases with age and correlates with the amount of plaques in the inner wall of Schlemm's canal. In cases of chronic simple glaucoma the amount of c.m. plaques did not significantly correlate with age, but the absolute amount of this material was significantly higher than in normal eyes. No correlation between inner wall and c.m. plaques was found, indicating that in glaucoma additional factors besides age contribute to plaque formation.

Quantitative analysis of 'plaque material' in the inner- and outer wall of Schlemm's canal in normal- and glaucomatous eyes

The amount of plaque material derived from the sheaths of the elastic-like fibers in the cribriform layer of the trabecular meshwork (sheath-derived or SD plaques) was quantitatively evaluated in normal eyes and in trabeculectomy specimens of chronic simple, intermittent angle closure, and pseudoexfoliation glaucoma. The amount of SD plaque material increases with age but no correlation between age and SD plaques was found in any of the glaucomas evaluated. In comparison to normal eyes, the amount of SD plaque material was significantly greater in cases of chronic simple glaucoma and in cases of intermittent narrow angle glaucoma, but not in pseudoexfoliation glaucoma. In the latter, number and distribution of SD plaques resembled those of normal eyes. SD plaques were also found in the outer wall of Schlemm's canal. In normal eyes there was a correlation between outer-wall plaques and age as well as between inner- and outer-wall plaques. These correlations were not found in the different types of glaucoma. Our findings indicate that in addition to the age-related increase in plaque material, there is in glaucomatous eyes some plaque material which is distributed unevenly in the inner- and outer-wall of Schlemm's canal. This additional material was not found in pseudoexfoliation glaucoma, indicating that elevated intraocular pressure alone can not be responsible for plaque formation.

Intraocular pressure and systemic blood pressure after administration of vasoactive substances in hypertensive and normal rats

Intraocular pressure (IOP) and arterial blood pressure (BP) were recorded manometrically in normotensive Wistar Kyoto rats (NR) and stroke-prone spontaneously hypertensive rats (SHR). IOP was significantly lower in SHR (7.8 +/- 0.2 mm Hg) compared to NR (15.9 +/- 0.4 mm Hg). In NR, administration of vasoactive substances (kallikrein, bradykinin, angiotensin I and II) or bloodletting resulted in significant IOP reactions, which ran nearly parallel to the acute BP changes. In SHR, however, IOP showed little reaction after comparable changes in BP. The cause of the low IOP in SHR is unknown. It is assumed that in SHR rarefaction of arterioles and capillaries and a decrease in the compliance of eye vessels, in combination with an increase in the distensibility of the bulbus at this low IOP level, contribute to the lack of IOP response after administration of vasoactive drugs.

Histoautoradiographic and electron microscopic studies on short-term explant cultures of the glaucomatous trabecular meshwork

Explant cultures of 15 trabeculectomy specimens derived from glaucomatous eyes were studied, using electron microscopy and histoautoradiography. The morphology of the trabecular meshwork was monitored for 3-14 days after explanation. In 4 cases the trabeculectomy specimens were cut in 2-3 pieces each and then incubated with 14C-glucosamine at different times during the observation period (2-10 days). The cells of the cribriform layer and the outer corneoscleral trabeculae become "activated" as soon as 3-4 days after explantation, developing a large amount of endoplasmic reticulum, Golgi material, and numerous mitochondria. Histoautoradiographically, intense labeling of the trabecular meshwork, especially the cribriform layer, was found after incubation with 14C-glucosamine. We assume that under tissue culture conditions the "activated" cells of the glaucomatous meshwork produce various types of glycosaminoglycans (GAGs) but, based on the experiments alone, no final conclusions can be made in this respect.

Comparative morphological studies on blood vessels in eyes of normotensive and spontaneously hypertensive rats

The spontaneously hypertensive rats (SHR) show a lower intraocular pressure--despite high arterial blood pressure--than the normotensive Wistar Kyoto rats (NR). In SHR the quantitative evaluation of resin casts and flat-mount preparations of the blood vessels of the ciliary body and choroid showed a significant dilation of the vessels when compared to NR. In the capillaries of the ciliary processes, as well as in the choriocapillaries, a vascular rarefaction was seen. In all regions of the ciliary body the number of fenestrations found in the endothelium of the capillaries was reduced by about half in SHR. In addition, hyalinization of the connective tissue--particularly around the vessels at the base of ciliary processes--was seen in SHR. The morphological changes of the vasculature and connective tissue described here may be considered the cause of the reduced aqueous formation and low intraocular pressure found in SHR.

Cellular structure of the conjunctival epithelium of rabbits

In rabbits, five different cell types were distinguished within the superficial cell layer of the conjunctival epithelium according to their ultrastructural appearance of cell organelles. These cell types also show a characteristic distribution within the various regions of the lids. The second cell type which is not found in the conjunctiva of primates is characterized by large osmiophilic granules. It is assumed that these cells are particularly important for the production of the lipid layer of the tear film preventing the rabbit cornea from evaporation.

Synthesis and composition of glycosaminoglycans by explant cultures of human ciliary body and ciliary processes in serum-containing and serum-free defined media

Freshly isolated ciliary body explants and tips of ciliary processes derived from human eyes were cultured in serum-containing or serum-free defined medium. These cultures synthesized tissue-bound and medium-released ("excreted") glycosaminoglycans (GAGs), as evidenced by the incorporation of 14C-glucosamine and enzymatic characterization of these labelled GAGs (hyaluronic acid, heparan sulphate, chondroitin sulphate, dermatan sulphate). The GAG synthesis and excretion rate was enhanced by serum. It is suggested that ciliary epithelium performs this function of GAG synthesis also under in vivo conditions.

Histoautoradiographic and biochemical studies on human and monkey trabecular meshwork and ciliary body in short-term explant culture

Explants of two types of chamber angle tissue derived from five human autopsy eyes and five freshly enucleated monkey eyes were kept under tissue culture conditions for 1-3 days and then incubated with labelled 14C-glucosamine for 40-48 h. In all specimens an intense labelling was seen histoautoradiographically within the area of the trabecular meshwork, especially in the cribriform layer and the outer wall of Schlemm's canal. Large quantities of silver grains were also found at the tips of the ciliary processes where the nonpigmented epithelium showed the most intense labelling. Measuring the total radioactivity of the two types of specimens in the tissue-localized and the medium-released glycosaminoglycans (GAGs), we found that the type 1 specimens containing only trabecular meshwork work and corneosclera "excrete" relatively more GAGs into the medium than the type 2 specimens consisting of corneosclera, trabecular meshwork and ciliary body. Biochemical analysis of these GAGs revealed that 57%-70% of the tissue GAGs were hyaluronic acid, 16%-33% heparan sulphate and 12%-22% various types of chondroitin sulphate. The findings show that both the ciliary epithelium and the trabecular meshwork possesses the ability to synthesize large amounts of GAGs, probably in the form of proteoglycans. The differences between the in vitro behaviour of type 1 and type 2 specimens indicate a functional interrelationship between the ciliary body and the trabecular meshwork, at least with regard to the GAG metabolism.

Why is intraocular pressure elevated in chronic simple glaucoma? Anatomical considerations

Ultrastructural analysis of 400 trabeculectomy specimens of glaucomatous eye revealed three types of extracellular deposits within the cribriform layer of the trabecular meshwork. One of these derives from the sheath of the subendothelial elastic-like fibres. Tissue culture and ultrahistochemical studies led to the assumption that these deposits contain glycoproteins, probably secreted by the cribriform layer cells.

Age-related changes in the composition of proteins in the trabecular meshwork of the human eye

The composition of the trabecular meshwork proteins of human eyes ranging in age from 36 days to 84 years was examined by polyacrylamide gel electrophoresis and amino acid analysis. Proteins of different molecular weights could be extracted from the tissue with acetic acid. Although their electrophoretic patterns became less distinct with increasing age, proteins of molecular weights ranging from 50 000 to 69 000 always prevailed. The amino acid compositions of the acetic acid-insoluble trabecular meshwork residues revealed the prevalence of collagenous proteins. The peptide maps produced by treatment with cyanogen bromide indicate that most of the fragments solubilized from the trabecular meshwork of younger eyes are derived from type I collagen. Beyond 40 years of age, the trabecular meshwork was resistant to cyanogen bromide and pepsin digestion. A rough estimate of the distribution of collagen types in the trabecular meshwork was based on 3-hydroxyproline/4-hydroxyproline ratios, indicating an age-related increase of type I collagen from about 55 to 70 per cent, and of type IV collagen from about 2 to 5 per cent of the total protein present. During ageing, some of the protein-bound methionine is oxidized to methionine sulfoxide, reaching about 35 per cent of the total methionine content at the age of 20 years and, with a slower rate of oxidation, a mean value of 40 per cent at 80 years of age. Electron-microscopic analysis of specimens remaining undissolved after cyanogen bromide cleavage and pepsin treatment no longer revealed regular collagenous fibrils but rather elastic-like fibers surrounded by wide sheaths consisting of fine fibrils with a regular cross-banding periodicity of 40-50 nm. In addition, clusters of so-called curly (lattice) collagen were found. The amino acid composition of this insoluble material suggests that altered collagen-like molecules prevail among the proteins of the residues.

Absorption of horse-radish peroxidase by the conjunctival epithelium of monkeys and rabbits

Horse-radish peroxidase was instilled into the conjunctival sac of rabbits and Cynomolgus monkeys. After an interval of 5, 30 or 60 min the conjunctival epithelium was studied by electron microscopy. The tracer was found to be absorbed predominantly by type-V cells, which are rich in mitochondria; this process was found to occur more rapidly in the rabbit than in the monkey. The particles were primarily incorporated into pinocytotic vesicles and phagosomes and were then either digested by phagolysosomes or transported through the basal portion of the surface epithelial cells into the expanding intercellular spaces distal to the junctional complexes.

Morphological studies on the regeneration of rabbit corneal endothelium under the influence of corticosteroids

In adult albino rabbits, the influence of corticosteroids on the regeneration of the corneal endothelium after cryocoagulation was studied using light-, scanning- and transmission electron microscopy. The follow-up period varied from 10 h to 10 days. In the regenerating endothelium, both mitotic and amitotic cells division were seen. In the dexamethasone-treated eyes, the regeneration process seemed to be stimulated rather than inhibited. In five of six eyes, areas of hyperproliferation were found, consisting of numerous elongated cells that formed several cell layers. Most of these cells revealed an extensively developed endoplasmic reticulum and Golgi apparatus as well as numerous mitochondria. There were signs of secretory activity. The mechanism for the development of these multilayered hyperproliferation zones is unknown.

Structural changes of human and monkey trabecular meshwork following in vitro cultivation

The entire chamber angle tissue of ten monkey eyes and nine normal human eyes was cultivated in organ cultures for 1-10 days and then investigated by electron microscopy. We found that the uveal and corneoscleral trabecular cells often degenerate as early as 2-3 days after explantation, whereas the cells of the cribriform region proliferate and show an increasing number of cell organelles (mitochondria, endoplasmic reticulum and Golgi complexes). Regarding the behaviour in vitro, we distinguished three different cell populations in the trabecular meshwork with probably different functions: (1) the endothelial cells of Schlemm's canal, (2) the trabecular cells of the cribriform region and (3) the uveal or corneoscleral trabecular cells.

Presence of matrix vesicles in the trabecular meshwork of glaucomatous eyes

In the last few years matrix vesicles (M.V.) have been found in the vessel wall in various diseases and are considered to be related with pathological changes of the extracellular fibers of the tissue (atypical collagen etc.). Since the trabecular meshwork, at least the cribriform region, may be looked upon as a part of a vessel wall, it was an obvious conclusion to look for M.V. even in this area. Lysosomal and non-lysosomal M.V. were found in 138 trabeculectomy-specimens of various kinds of glaucoma, located for the most part within the cribriform or juxta-canalicular region of the meshwork. In ten cases small, electron-dense M.V. were found which ultrahistochemically showed a positive reaction for acid phosphatase. This proves that these vesicles are indeed extracellular lysosomes.

Synthesis and composition of glycosaminoglycans by cultured human trabecular meshwork cells

A human trabecular meshwork cell line with a limited number of population doublings was established in monolayer culture. All cultures produced hyaluronic acid, heparan sulfate, chondroitin sulfate, and dermatan sulfate. Following [14C]-glucosamine incorporation into proliferating (phase II) cultures, 70%--80% of the medium glycosaminoglycan label was found in hyaluronic acid and 8%--14% in heparin sulfate. About 60% of the cell-bound activity was associated with hyaluronic acid and 30% with heparan sulfate. Long-term cultivation under nondividing ("senescent") conditions resulted in a change of the pattern of synthesized and excreted (medium) [14C]-glucosamine-labeled glycosaminoglycans with a relative decrease of hyaluronic acid and a relative increase of heparan sulfate.

Specialized cell types and their regional distribution in the conjunctival epithelium of the cynomolgus monkey

In the superficial layer of the conjunctival epithelium of cynomolgus monkeys, five different cell types were found. The cell types were distinguished by ultrastructural criteria (e.g., cell organelles and cytoplasma) and are defined as follows: type I are the goblet cells; type II is characterized by the content of small electron-dense granules type III is particularly rich in Golgi material, type IV contains a specifically large amount of ER; type V shows an exceptionally large number of mitochondria. The quantitative evaluation of these cell types in 15 areas of the conjunctiva of 3 animals revealed a characteristic pattern of regional distribution, which may reflect the otherwise unknown functional significance of most of these cell types.

The fine structure of the cribriform meshwork in normal and glaucomatous eyes as seen in tangential sections

Electron microscopic serial sections in a tangential plane through the inner wall of Schlemm's canal and the trabecular meshwork in normal and glaucomatous eyes revealed a characteristic network of elastic-like fibers (cribriform plexus), which is directly connected to the inner wall endothelium by a special fiber system (connecting fibrils). This cribriform plexus is also connected to the ciliary muscle system. Ciliary muscle tendons were found that not only show the same fine structure as the cribriform plexus but also join it. The ciliary muscle tone can therefore directly influence the fiber system of the cribriform plexus and its connections to the inner wall of Schlemm's canal. in eyes with chronic simple glaucoma, three types of plaques in the cribriform meshwork have been described after studies of sagittal sections. A comparison with tangential sections of the same piece of tissue shows that plaques of type II and III are in fact sections through the cribriform plexus and that only type I plaques are a separate entity.

Ultrahistochemical studies on tangential sections of the trabecular meshwork in normal and glaucomatous eyes

The composition of the extracellular material of the cribriform meshwork was compared in five normal and 13 glaucomatous eyes of the same age group (58 to 70 years). Enzymatic digestion and histochemical methods applicable to electron microscopy were used. In both groups of eyes the ground substance was sensitive to chondroitinase ABC, and also the other methods showed no qualitative differences between the groups. In contrast, the fibrillar components of the extracellular material, which partly could be studied only after enzymatic treatment, showed qualitative differences between normal and glaucomatous eyes. In addition to the normal fibrous components, the glaucoma tissue contained large amounts of very fine fibrils. In seven eyes with end-stage glaucoma these fibrils filled the whole cribriform region. In these cases collagen fibers also appeared. Whether these were formed from the fine fibrils is not clear.

Experimental studies on the influence of the kallikrein-kinin system on glucose utilization

Our studies, together with the findings of other authors, indicate that kallikreins, via kinin release, play a role in glucose metabolism. It is most likely that the utilization of glucose is enhanced directly within the energy metabolizing cell itself but not indirectly by way of an insulin release in the pancreatic islets, since the in vitro studies on isolated islets of Langerhans did not reveal any effect of bradykinin on insulin secretion or insulin release. Further investigations are, however, necessary to clarify to what extent and in what way the kallikrein-kinin system is involved in causing the increased glucose utilization.